Abstract/Project Summary: In the United States alone influenza virus is a major health burden, hospitalizing 200,000, and resulting in 36,000 deaths per year. Pandemic influenza strains also have the potential to cause much more severe disease and mortality as in the case of the 1918 Spanish Flu. Given that the seasonality of infection is driven largely by antigenic shift to avoid established antibody responses, the creation of a broadly active T cell-based vaccine that recognizes highly conserved internal epitopes is an appropriate strategy to circumvent this issue. Lung tissue resident memory T cells (lung TRM) have already been found to be important in a protective heterosubtypic response to influenza, but the mechanisms by which they are established are still unknown. This project will use a mouse model of influenza infection to examine the role of monocytes and other antigen- presenting cell (APC) subsets in the generation of a protective lung TRM response. This will be accomplished using both genetic and antibody depletion approaches to eliminate specific APC subsets in order to investigate the role of these cells for the generation of tissue resident memory T cells. Using a combination of flow- cytometry and in vitro T cell stimulation, the goal of this proposal is to determine the contribution of individual APC subsets in establishing cellular immunity against a secondary influenza challenge. The knowledge gained in this study may guide future vaccine design against respiratory pathogens by defining the optimal APC targets for the delivery of antigen in order to generate lung TRM.